async function async1(){
  console.log('async1  start');
  await async2()  //浏览器版本更新，把await把他提前了
  console.log('async1 end');
} 

async function async2(){
  console.log('async2');
}

async1()
console.log('start');

//浏览器版本更新，把await把他提前了,如果是以前浏览器就是下面的顺序
// async1  start
// start
// async2
// async1 end